It really depends on what you mean by disposable spends.
After we, as a family, have paid all bills, we have £large amount left.
We then put £large amount into various savings accounts and investments for each of us solely, joint accounts and accounts for our children. This is about 80% of our income, and I suppose is technically "disposable", but we don't really see it as such.
We then spend £very comfortable amount for stuff relating to the family - days out/eating out/bits and bobs/stuff for the house/general family spends.
DH and I give ourselves £100 a month each for "personal spends". It's a small amount because we literally have virtually no "personal" costs, as pretty much everything we do is family related. Essentials such as dental/optical/clothes/haircuts etc would come out of the family spends account. Really, its for buying each other presents so that they don't show up on the joint account, and so that we both have a current account in our own names just in case we need it for some reason (bank accounts frozen due to fraud etc is what we were thinking, not that it has ever happened.)
This is an unanswerable question really, as what counts as "disposable" varies from family to family, and what amount is "personal" will also vary from family to family.